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Earliest humans suffered through massive volcanic blasts

Geologists think our ancestors, making their way through East Africa, had to contend with devastating lava flows and poisonous gases. Belinda Smith reports.

Satellite image of Aluto volcano, located in Ethiopia’s Rift Valley. The volcano is nestled between the lakes of Ziway (to the north) and Langano (south), the dark areas on the volcano represent lava flows.

William Hutchison (University of Oxford) / NASA

When the first group of Homo sapiens reached Ethiopia some 200,000 years ago, they were greeted by massive volcanic explosions that blasted poisonous ash and gas for millennia, new research suggests.

Geologists from Ethiopia, the US and UK examined ancient lava flows in the East African Rift and found a 200-kilometre stretch pulsed with huge eruptions of magma between 320,000 and 170,000 years ago – right when the first modern humans reached the region.

The East African Rift system is an active continental rift, and has been for around 20 million years.

It runs down the east side of the African plate and is slowly but inexorably splitting it in two at the rate of a few millimetres each year.

Geologists suspect that within 10 million years, the Earth’s crust and upper mantle layers (collectively known as the lithosphere) will unzip along the rift, creating two new plates – the Somali and Nubian Plates.

In such rifts, where the lithosphere is thin and dotted with weak points, the underlying magma is – at times – able to more easily burble to the surface in pulses.

William Hutchison from the University of Oxford and colleagues reconstructed the volcanic history of the rift to find out when these pulses occurred.

Since the region is linked with early human evolution, did our ancestors have to contend with explosive volcanic activity? And if so, were the eruptions large and devastating enough to affect hominin migration?

The caldera walls of Corbetti volcano, Ethiopia. The caldera was created 200,000 years ago during a colossal volcanic eruption.

William Hutchison (University of Oxford)

Hutchison and his crew dated rocks thrown out by the caldera-forming eruptions at Aluto and Corbetti volcanoes, two major volcanoes in Ethiopia on the East African Rift.

Massive layers of volcanic rock, tens to hundreds of metres thick, pointed to colossal blasts that spewed enormous amounts of magma in a relatively short period.

When they combined data with that from other rift volcanoes, the researchers narrowed their estimations to a burst of highly explosive volcanism between 320,000 and 170,000 years ago along the segment – a rate five times higher than the average rate of volcanism for the rift.

The volcanoes were not directly connected, but the underlying magma heaving from the mantle to the crust was the likely driver behind the pulses.

More geochemical investigations should uncover if this was the case, the researchers write.

The researchers also suggest volcanic activity would have dramatically changed the landscape and environments occupied by our earliest human ancestors.

“The major explosive volcanic eruptions discussed here […] would have caused rapid and profound environmental disruption in the region,” they write.

“Ash, acidic gases and aerosol released from such events would have affected rift lakes and vegetation causing a cascade of environmental disruption, remodelling the landscapes and resources on which hominins depended.”